The invention relates to writing instruments having a foam layer and methods of making such instruments.
Articles that are gripped with the fingers have been provided with resilient or cushioned surfaces to improve the comfort and feel of the article to the user. In particular, writing instruments have been provided with gripping devices designed to provide a comfortable gripping area. For example, some writing instruments include a sleeve of resilient compressible material, e.g., a foam, in the gripping area of the writing instrument. The sleeve may be applied by sliding it onto the writing instrument.
The invention features writing instruments that have a barrel including a foam layer covering the outer surface of a preformed tubular core. The foam layer has good resistance to skin oils and perspiration, and thus exhibits good durability over the life of the writing instrument. Preferred foam layers have desirable tactile properties and are sufficiently soft so as to provide good user comfort, while being sufficiently hard so that the user does not feel the underlying core through the foam layer.
The invention also features methods of making these writing instruments. The methods of the invention allow foamable materials that will provide these properties to be applied to a preformed core without distortion of the core. The methods of the invention also allow such foamable materials to be foamed in a controlled manner that will result in a foam layer having a desired texture and cell size distribution.
In one aspect, the invention features a method of making an elongated tubular article. The method includes passing a tubular core comprising a first material through a die having an exit, introducing a second material into the die, and foaming the second material at the exit of the die, to form the tubular article having a foam layer surrounding the tubular core. The foam layer has a substantially uniform cell size distribution in the radial direction.
The method can further include extruding a polymeric material to form the tubular core, and/or passing the tubular article through a radially adjustable end piece that is constructed to distribute the foam layer uniformly around the circumference of the tubular core.
In another aspect, the invention features a method of making a barrel for a writing instrument. The method includes passing a preformed tubular core having a first material through a die having an exit, introducing a second material into the die, foaming the second material at the exit of the die, to form a foam layer surrounding the tubular core, and cutting the tubular core and foam layer to a predetermined length, to form a writing instrument barrel having a foam gripping surface.
Embodiments of the invention can include one or more of the following features. The foam layer can be embossed and/or marked. An additive can be added to the second material, which can include a foamable, partially cross-linkable polymer comprising a blend of polypropylene and EPDM rubber. The method can further include inserting an ink refill into the barrel to form the writing instrument. The method can further include partially cross-linking the polymer during foaming.
The invention also features a method of forming a foamed layer on a preformed tubular core. The method includes drawing the preformed tubular core through a die. The die has a cavity defined between an outer member and an inner member, an inlet to the cavity, for feeding the foamable material into the cavity, and a die exit. The inner member defines a lumen through which the preformed elongate member can be drawn. The method further includes introducing a foamable material into the cavity under conditions that will cause the foamable material to foam upon exiting the die exit and form a foamed layer around the outer surface of the preformed tubular core. The inner member has an outer surface, facing the cavity, that is configured to cause substantially uniform flow of the foamable material around the inner member.
The die exit is configured to prevent foaming of the foamable material until the foamable material has exited the die. For example, the die exit can have an aspect ratio of less than one, preferably less than 0.1. The die exit can have an exit angle of about 140 to 180 degrees.
The outer surface can include a ramped diverter, which can be positioned facing the inlet. The diverter can have a teardrop shape.
Additionally, the invention features a die for extruding a foamable material onto a preformed core during pultrusion. The die includes a cavity defined between an outer member and an inner member, an inlet to the cavity, for feeding the foamable material into the cavity, and a die exit. The inner member can define a lumen through which the preformed core can be drawn, and have an outer surface, facing the cavity, that is configured to cause substantially uniform flow of the foamable material around the inner member.
Embodiments of the die can include one or more of the following features. The die can be configured to prevent foaming of the foamable material until the foamable material has exited the die. The die exit can be configured to have an aspect ratio of about one, or less than one, or approximately zero. The die exit can be configured to have an exit angle of about 140 degrees to about 180 degrees. The outer member can define the die exit.
The die can include a face plate, which can define the die exit. The face plate can be removable and replaceable.
The die can further include a diverter on the inner member constructed to provide substantially uniform flow of the foamable material around the inner member.
The inner member can include an end plate, and the diverter can have a surface angled between about 30 degrees and about 60 degrees, preferably about 45 degrees, relative to a plane perpendicular to the longitudinal axis of the lumen.
The die can also include a second diverter positioned on the inner member, for causing substantially uniform flow of the foamable material around the inner member. The second diverter, which can have a teardrop shape, can be positioned opposite the inlet.
The die can include an end piece adjacent to the die exit for uniformly distributing the foamable material around the preformed core. The end piece can have a radially adjustable ring member.
The invention further features a writing instrument having a tubular core and a foam layer on the tubular core. The foam layer includes a partially cross-linked polymer having a blend of polypropylene and EPDM rubber. The foam layer can have a substantially uniform pore size in the radial direction. The tubular core can include polypropylene.
The foam layer can have a color additive.
The foam layer can have a foam density of about 0.1 g/cm3 to about 0.9 g/cm3, or about 0.4 g/cm3 to about 0.5 g/cm3.
The foam layer can cover substantially the entire outer surface of the tubular core.
The invention also features a method of making a barrel for a writing instrument including extruding a tubular core, and applying a foam layer to the core using a pultrusion process.
Other features and advantages of the invention will be apparent from the description and drawings, and from the claims.